A hard drive is a non-volatile storage device that stores digitally encoded data on rotating platters with an associated magnetic surface. As shown in FIG. 1, a hard drive 100 includes a spindle 101 that holds at least one platter 102 having a magnetic surface 104, which spins at a constant speed (e.g., 10,000 revolutions per minute (rpm), 7,200 rpm, or 5,400 rpm). To write data onto a rotating platter, a portion of the magnetic surface 104 is magnetized via a magnetic write head 106. The write head 106 is coupled with an actuator arm 108 that moves radially across the spinning platters 102. To create a current pulse to control the write operation, a differential hard drive write system 110 including a hard drive controller 112 is coupled to the write head 106. The hard drive controller 112 is configured to control the read and/or write operations via a hard drive write system 110.
To increase hard drive write speed and capacity, the hard drive write system 110 generates narrow current pulses via a differential control pulse to write information to the magnetic surface 104. However, as the duration of the current pulse decreases to accommodate increased hard drive speed and storage capacity, the current pulse becomes distorted during transmission to the write head 106. To correct the distorted edge of the current pulse, the hard drive write system 110 produces current pulses with an overshoot portion to prevent distortion to the leading edge of the current pulse. The overshoot portion is followed by a sustain portion to write information to the platter for the full duration of the write operation.
As appreciated by a person with ordinary skill in art, the hard drive operation results in a significant amount of heat. Generally, hard drives may achieve temperatures of up to 130° C. The increased temperature of the hard drive affects performance of the devices in the write driver system 110. Temperature in the hard drive 100 affects performance of devices and causes the parasitics and parameters of the devices to vary either in a linear or non-linear fashion. For example, resistors and stray, parasitic resistances vary over temperature.
Another example of how device performance varies is an NPN transistor, which experiences reduced switching speed due to increased temperature. In other words, as temperature increases, switching time between transistors increases and results in slower transmission of the overshoot current pulse between devices. As illustrated in FIG. 1B, the overshoot current pulse 120 has a sharp leading edge 122 and delayed switching time between transistors results the loss and degradation of the leading edge 122. The solid line illustrated in FIG. 1B shows the ideal current pulse, but the dashed line shows how the current pulse degrades with temperature. Consequently, the amplitude and the duration of the overshoot current pulse is reduced in the write drive system.